Engines, for example IC engines burning gasoline, diesel or biofuel, output various harmful substances which must be treated to meet current and future emissions legislation. Most commonly those substances comprise hydrocarbons (HC), carbon monoxides (CO), mono-nitrogen oxides (NOx) and particulate matter, such as carbon (C), a constituent of soot. Some of those substances may be reduced by careful control of the operating conditions of the engine, but usually it is necessary to provide an emissions cleaning module downstream of the engine to treat at least some of those substances entrained in the exhaust gas. Various apparatus for reducing and/or eliminating constituents in emissions are known. For example, it is known to provide an oxidation device, such as a diesel oxidation catalyst, to reduce or to eliminate hydrocarbons (HC) and/or carbon monoxide (CO). Oxidation devices generally include a catalyst to convert those substances into carbon dioxide and water, which are significantly less harmful. As a further example, emissions cleaning modules may include a particulate filter to restrict the particulates present in the exhaust gas from being output to atmosphere.
By use of an emissions cleaning module, engine emissions can be cleaned, meaning that a proportion of the harmful substances which would otherwise be released to atmosphere are instead converted to carbon dioxide (CO2), nitrogen (N2) and water (H2O).
In addition, it is known to reduce or eliminate mono-nitrogen oxides (NOx) in diesel combustion emissions by conversion to diatomic nitrogen (N2) and water (H2O) by catalytic reaction with chemicals such as ammonia (NH3) entrained in the exhaust gas. Generally ammonia is not present in exhaust gas and must therefore be introduced upstream of a catalyst, typically by injecting a urea solution into the exhaust gas which decomposes into ammonia at sufficiently high temperatures.
By these methods, engine emissions can be cleaned, meaning that a proportion of the harmful substances which would otherwise be released to atmosphere are instead converted to carbon dioxide (CO2), nitrogen (N2) and water (H2O).
Emissions cleaning modules may also comprise an injector module for injecting a fluid, such as urea, into the engine emissions flow. It is also know to include a mixer module to aid mixer of the injected urea with the engine emissions flow. For example, US2010/0257850 describes an emission cleaning module having a mixer pipe. The mixer pipe is comprised of inner and outer pipes which are overlapped with each other in a relatively stretchable and retractable manner. The inner pipe is fixed at a right-hand end to a housing and the outer pipe is secured to an outer periphery of the inner pipe part-way along its length. A sliding seal is provided at an opposite end of the inner pipe. The structure of the mixer module of US2010/0257850 is relatively complicated.
Against this background there is provided an emissions cleaning module comprising an improved arrangement of mixer module.